Heat engines generally, in order to run under optimum conditions, need to be cooled constantly while they are running. For a very long time, water- or air-cooling circuits have been developed, these being supposed to keep the immediate surroundings of the combustion chambers at a temperature which never exceeds the highest temperature compatible with the integrity of the static or moving mechanical parts present in the engine.
Frequently, at the present time, the search is on to improve the isolation of engine compartments, so as to limit the odours given off and the transmission of vibration and undesirable noises. These new requirements, coupled with the fact that the empty space within engine compartments has tended to decrease because of the development of compact, lightweight vehicles, are partly responsible for the net temperature rise in the environment of the engine within the compartment.
Something else which is responsible for this rise in temperature has been the tendency to incorporate, around modern engines, an increasing number of accessories, such as the air compressor or turbocharger which operate at very high temperatures and generate additional hot spots in the engine compartment.
The result of this is a danger of excessive heating of the environment in the engine compartment which conventional cooling circuits will not be able to limit completely.
It has therefore become desirable to supply means of cooling this environment in order not to harm the overall efficiency of the engine and not to endanger the mechanical performance of certain components and accessories in its immediate vicinity.
For example, it has been proposed that a duct be fitted in the compartment to convey the fresh air drawn in by the cooling circuit fan towards the rear of the engine compartment so as to better distribute the inrush of fresh air throughout the volume of the compartment (French patent application 2667549).
Japanese patent application JP-08/164756 describes a motor vehicle bonnet which, on its internal face, has a broad, flat duct conveying fresh air taken from the front face of the vehicle towards the rear part of a transverse engine.
These various systems do, however, have the drawback of cooling only one of the hot zones of the environment. Furthermore, the flow rate and, therefore, the cooling efficiency of such systems are still low because they are confined to introducing fresh air and do not directly remove the energy from the hottest spots of the environment in the compartment.
The object of the invention is therefore to provide a device which cools all of the hotter zones of the environment in an engine compartment, whether these be moving or static parts, with satisfactory efficiency and which makes it possible to use various materials from which to make the peripheral components and accessories of the engine.